Analog Inputs; Reference Options; External Connectors - Analog Devices EVAL-AD7492SDZ User Manual

UG-371

ANALOG INPUTS

The analog input to the evaluation board can be either the SK1
SMB (push on) connector with a unipolar signal source or the
SK3 SMB (push on) connector when using a bipolar signal source.
The unipolar input is buffered with dedicated circuitry (U3)
and discrete components, as shown in Figure 3.
LK15 can be used to put a 50 Ω impedance matching load on the
input. LK10 is placed in Position B to connect the output of U3
to the AD7492.
The bipolar signal is buffered with dedicated circuitry (U4, U6,
and U9) along with the discreet components shown in Figure 4.
The circuit shown in Figure 4 allows for different configurations,
and an external source can be applied to bias the input voltage.
The analog input buffer amplifier (U3) is set as a unity gain buffer.
The amplifier positive rail is driven from ±5 V (from
U801, that is used to drive a dual rail, power supply, SEPIC Cuk
configuration), which can be changed to a different value, as
required, by using the external terminals on J800. LK801 and
LK802 must be set to Position B to drive the amplifiers from an
external source. For dynamic performance, an FFT test can be
done by applying a very low distortion ac source.
C11 C2
10µF 0.1µF
R2
SK1
130Ω
UNIPOLAR
VIN
INPUT SIGNAL
LK15
R5
51Ω
Figure 3. Unipolar Input Buffer Circuitry
Figure 4. Bipolar Input Buffer Circuitry
ADP1613,
VDD_+5V
R12
130Ω
C10
22pF
U3
2
7
–
V+
6
B
OP
3
V–
+
AD8597ARZ
4
A
VIN
LK10
C8 C16
10µF 0.1µF
VIN_BIASED
VDD_–5V

REFERENCE OPTIONS

The reference source can be from the
the ADR431 ultralow noise XFET® voltage reference device (U5).

EXTERNAL CONNECTORS

Table 4 lists the connector functions of the evaluation board.
Table 4. Connector Functions
Connector
EXT_OFFSET
J3
J700
J702
J703
J800
SK1
SK2
SK3
Rev. 0 | Page 6 of 24
EVAL-AD7492SDZ User Guide
AD7492
VIN
AD7492
Function
SMB socket for external bias input, which
provided that LK20 is correctly configured, can
be applied to U6
External VDRIVE screw terminal connector
7 V to 9 V bench supply screw terminal connector
7 V to 9 V dc transformer power connector
AVCC screw terminal connector
VSS and VDD screw terminal connectors
Unipolar signal input SMB socket
CONVST signal input SMB socket
Bipolar signal input SMB socket
REF OUT pin or